Production of nitric acid



Aug. 20, 1940. N. TlTLEsTAD ET AL PRODUCTION OF NITRIC ACID Filed Jan.20, 1939 HMH.

Patented Aug. 20, 1940 "Unirse STATES PRODUCTION or Nrrnlc ACID NicolayTitlestad, White Plains, N. Y., and Arthur C. Bright,Piney River, Va.,assignors to Ghemical Construction Corporation, NewYork, N. Y., acorporation of Delaware Application January 20, 1939, serial No. 251,882

3 Claims;

Oxides for the subsequent pressure absorption of the sameto producenitric acid.

The apparatus involved in a known nitric acid system is comprisedessentially and in the order named, of an ammonia burner containing aplatvinum `gauze catalyst, a cooler such as a waste heat boiler, acondenser, a compressor, an oxidizer and a pressure absorption tower.

The process of producing nitric acid in such a system comprises thefollowing sequence of steps. Ammonia is oxidized with air on theplatinum gauze to produce a hot gas containingnitric oxide and watervapor and this hot gas coming from the ammonia burner is cooled and heatrecovered therefrom in the form of steam by passing the hot gas througha waste heat boiler. Thereafter the partially cooled gas is passedthrough a condenser operated at relatively low temperatures to remove amajor part of the water therefrom, whereupon the gases in a separatestep are compressed to a high pressure, for eX- ample to severalatmospheres, subjected to an oxidation step if necessary, and thenabsorbed in the tower with a. weak nitric' acid and/or water` underthepressure produced by the compression step.

In plants employing the above process the gas is ordinarily compressedby a centrifugal or reciprocal type compressor. Centrifugal compressorshave been used in large capacity plants, but they are not economical inplants of low capacity, i. e., those having a small gas volume due to`their high initial cost. Reciprocal type compressors have beensuggested as a substitute in smaller plants, but the problem oflubricating the pistons of such compressors is still a serious one. Oneof the chief difculties in the lubrication of this type of compressor isthe destruction of the lubricant due to its carbonization by the nitricacid formed when compressing the moist nitrogen oxides.

-trated diagrammatically an apparatus designed for the carrying out ofour invention and in which Fig. 1 is a representation of a nitric acidsystem showing one type of hydraulic compressor and Fig. 2 is a modiedform of hydraulic compressor. I It is to be understood that all theparts of such a nitric acid system are not illustrated in the drawingbut only those necessary to point out the invention. f

Referring to Fig. 1 there is diagrammatically E10 showntherein anammonia burner containing a suitablecatalyst such as platinum gauzetogether with a waste heat boiler, an hydraulic compressor denotedgenerally at I, an oxidizer and a high pressure absorption4 tower. V'Ihehydraulic com- "T5,

pressor I consists of an aspirator head 3 of standard construction, avertical feed pipe It for carry- `ing Ycompressing liquid thereto, awater cooling jacket 5 on pipe Q, and a centrifugal pump 6 connected atits discharge sideV with pipe li. A pipe 'l is shown connected to thedischarge side of the aspirator head 3 and with a gas and liquidseparation tank 8 of a construction suitable for the disengagement ofthe compressed gases from the compressing liquid. Pipes 9 and'2`5 l0 areshown as connected to the tank il and to the oxidizer and absorptiontower respectively for Athe passage of disengaged and compressed gas onthe one hand and a portion of the liquid from tank 8 on the other hand.Pipe I i is provided for the return by means of centrifugal pump 6 ofliquid from the tank 8 to the compressing cycle. A means is provided forthe introduction of water into the ksystem for use as initialcompressing liquid; such a means may be that as indicated on line |.lbetween the pump 6 and the separation tank 8.

Assuming that ammonia has been oxidized with the reaction proportion ofair in the ammonia burner to give a hot gas containing nitrogen oxideand water vapor and that the hot gas has been partially cooled in thewaste heat boiler, the operation of the hydraulic compressor to removewater from and to compress the gases in accordance with my inventionisas follows: 45

The hot gas from the waste heat boiler is passed through pipe 2 andenters the aspirator head 3 at an elevated temperature and preferablyabove the dew point of the gas. In the aspirator' head the hot gas willencounter a stream of cool weak nitric acid supplied by pum-p 6 throughpipe 4, the acid moving at a velocity head suflicient for the aspirationand compression of the gas. The centrifugal pump will be operated at apressure volume of weak acid sufficient 55 to create the necessaryvelocity head, and the rapidly moving stream of weak nitric acid in theaspirator head will be cooled and mixed therewith, the mixture of gasand acid moving down through pipe 'l into separation tank 8 where thecompressed gas will be disengaged from the compressing acid and thecondensed water. 'Ihe separated compressed gas will then be passedthrough pipe 9 to the oxidizer and eventually to the absorption towerwhile some of the weak acid from the separation tank will be passed tothe absorption tower for the absorption therein of the compressed andoxidized nitric oxide under the high pressure resulting from thecompression of the gas to produce nitric acid. The oxidizer andabsorption tower may be operated in accordance with known practice.

In Fig. 2 we have shown a modiiied design of hydraulic compressor foruse in the above described nitric acid systems and in which the 2 fromthe waste heat boiler will be cooled by a Water jacket i3 and Watercondensed therefrom before they enter the aspirator head. A chamber isshown at i4 and a pipe at i5 for the collection and removal of condensedwater to an absorption tower. In this modification the gas and liquidseparation tank I6 is not provided with a pipe for removal of liquidtherefrom to an absorption tower since we contemplate the removal ofsufcient water from the gas by cooler I3.

The design of the gas and liquid separation tank is such as to allow ofdisengagement of the compressed ygas from the acid and it conceivablymay take the form of a flash separator or of a single chamber in whichmay take place the disengagement of the gas from the compressing acidand absorption of the separated gas to produce nitric acid.

From the foregoing it will be seen that a speciiic embodiment of theinvention has been described which accomplishes all the objects thereof.This embodiment has been described as operating-on oxides of nitrogenfrom the catalytic oxidation of ammonia, since this is a representativegas source. It should be understood, however, that the invention isequally well adapted to the compression and subsequent oxidation andabsorption of oxides of nitrogen from other sources, such as from thedenitration of spent nitrating acid, from the arc process, or in generalfrom any source in which oxides of nitrogen are produced in commerciallyuseful quantities.

It should also be understood that the invention in its broader aspectsis not restricted to the specific details which have been described andshown, b-ut that it is limited only by the scope of the followingclaims.

What we claim is:

1. An apparatus for the production of nitric acid comprising incombination an ammonia burner, a gas cooler, an hydraulic compressordirectly connected with the gas outlet of the 'gas cooler, the hydrauliccompressor comprising a centrifugal pump, anaspirator head, a verticalconduit connecting the pump with the aspirator head, means for coolingthe aqueous compressing liquid, an oxidizer, and a pressure absorptiontower.

2. A process of producing nitric acid which comprises condensing waterfrom and compressing a relatively cool gas containing lower oxides ofnitrogen in a single operation by hydraulically compressing it with acool aqueous liquid moving under pressure, disengaging the compressedgas from the compressing liquid, oxidizing lower oxides of nitrogen inthe gas to nitrogen peroxide, and absorbing the nitrogen peroxide in anaqueous absorbing medium under pressure to form nitric acid.

3. A process of producing nitric acid which comprises oxidizing ammoniato form a hot gas containing lower oxides of nitrogen and water Vapor,partially cooling saidgas, condensing water from and compressing saidpartially cooled gas in a single operation by hydraulically compressing.it with a cool aqueousv liquid moving under pressure, disengaging thecompressed gas from the compressing liquid,` oxidizing nitric oxide inthe compressed gas to nitrogen peroxide, and absorbing the nitrogenperoxide in the gas under high pressure to form nitric acid.

NICOLAY TITLESTAD. ARTHUR) C. BRIGHT.

